The program in Radiobiology & Radiotherapy (RR) comprises a broadly based, multifaceted research effort in radiation therapy, radiation biology, radiological physics and related areas of tumor biology. This program has been an approved component of the Yale Cancer Center Grant for over 25 years. Its long-term goal is to improve the treatment of cancer in general and in particular, the effectiveness of radiation therapy. The program includes a broad spectrum of activity that extends from laboratory-based experimental research to clinical investigation, and features investigators associated with 16 departments. Some of the key themes include studies of carcinogenesis, genetic instability and cell growth control; elucidation of DNA repair pathways; investigation of tumor hypoxia and development of hypoxia-targeted cancer therapies; molecular correlations with outcomes in radiation therapy; and improvements in radiation dosimetry, imaging, and delivery. The majority of RR members have rich interactions with the Yale Cancer